Slack users horrified to discover messages used for AI training

Slack users horrified to discover messages used for AI training reader comments 53

After launching Slack AI in February, Slack appears to be digging its heels in, defending its vague policy that by default sucks up customers' data—including messages, content, and files—to train Slack's global AI models.

According to Slack engineer Aaron Maurer, Slack has explained in a blog that the Salesforce-owned chat service does not train its large language models (LLMs) on customer data. But Slack's policy may need updating "to explain more carefully how these privacy principles play with Slack AI," Maurer wrote on Threads, partly because the policy "was originally written about the search/recommendation work we've been doing for years prior to Slack AI."

Maurer was responding to a Threads post from engineer and writer Gergely Orosz, who called for companies to opt out of data sharing until the policy is clarified, not by a blog, but in the actual policy language.

"An ML engineer at Slack says they don’t use messages to train LLM models," Orosz wrote. "My response is that the current terms allow them to do so. I’ll believe this is the policy when it’s in the policy. A blog post is not the privacy policy: every serious company knows this."

The tension for users becomes clearer if you compare Slack's privacy principles with how the company touts Slack AI.

Slack's privacy principles specifically say that "Machine Learning (ML) and Artificial Intelligence (AI) are useful tools that we use in limited ways to enhance our product mission. To develop AI/ML models, our systems analyze Customer Data (e.g. messages, content, and files) submitted to Slack as well as other information (including usage information) as defined in our privacy policy and in your customer agreement."

Meanwhile, Slack AI's page says, "Work without worry. Your data is your data. We don't use it to train Slack AI."

Because of this incongruity, users called on Slack to update the privacy principles to make it clear how data is used for Slack AI or any future AI updates. According to a Salesforce spokesperson, the company has agreed an update is needed.


"Yesterday, some Slack community members asked for more clarity regarding our privacy principles," Salesforce's spokesperson told Ars. "We’ll be updating those principles today to better explain the relationship between customer data and generative AI in Slack."

The spokesperson told Ars that the policy updates will clarify that Slack does not "develop LLMs or other generative models using customer data," "use customer data to train third-party LLMs" or "build or train these models in such a way that they could learn, memorize, or be able to reproduce customer data." The update will also clarify that "Slack AI uses off-the-shelf LLMs where the models don't retain customer data," ensuring that "customer data never leaves Slack's trust boundary, and the providers of the LLM never have any access to the customer data."

These changes, however, do not seem to address a key concern for users who never explicitly consented to sharing chats and other Slack content for use in AI training.

Users opting out of sharing chats with Slack

This controversial policy is not new. Wired warned about it in April, and TechCrunch reported that the policy has been in place since at least September 2023.

But widespread backlash began swelling last night on Hacker News, where Slack users called out the chat service for seemingly failing to notify users about the policy change, instead quietly opting them in by default. To critics, it felt like there was no benefit to opting in for anyone but Slack.

From there, the backlash spread to social media, where SlackHQ hastened to clarify Slack's terms with explanations that did not seem to address all the criticism.

"I'm sorry Slack, you're doing fucking WHAT with user DMs, messages, files, etc?" Corey Quinn, the chief cloud economist for a cost management company called Duckbill Group, posted on X. "I'm positive I'm not reading this correctly."

SlackHQ responded to Quinn after the economist declared, "I hate this so much," and confirmed that he had opted out of data sharing in his paid workspace.

"To clarify, Slack has platform-level machine-learning models for things like channel and emoji recommendations and search results," SlackHQ posted. "And yes, customers can exclude their data from helping train those (non-generative) ML models. Customer data belongs to the customer."

Later in the thread, SlackHQ noted, "Slack AI—which is our generative AI experience natively built in Slack—[and] is a separately purchased add-on that uses Large Language Models (LLMs) but does not train those LLMs on customer data."

Opting out is not necessarily straightforward, and individuals currently cannot opt out unless their entire organization opts out.

"You can always quit your job, right?" a Hacker News commenter joked.

And rather than adding a button to immediately turn off the firehose, Slack instructs customers to use a very specific subject line and contact Slack directly to stop sharing data:

Contact us to opt out. If you want to exclude your Customer Data from Slack global models, you can opt out. To opt out, please have your org, workspace owners or primary owner contact our Customer Experience team at [email protected] with your workspace/org URL and the subject line ‘Slack global model opt-out request’. We will process your request and respond once the opt-out has been completed.

"Where is the opt-out button?" one Threads user asked Maurer.

Many commenters on Hacker News, Threads, and X confirmed that they were opting out after reading Slack's policy, as well as urging their organizations to consider using other chat services. Ars also chose to opt out today.

However, it remains unclear what exactly happens when users opt out. Commenters on Hacker News slammed Slack for failing to explain whether opting out deletes data from the models or "what exactly does the customer support rep do on their end to opt you out."

"You can't exactly go into the model and 'erase' parts of the corpus post-hoc," one commenter suggested.

All Slack's privacy principles state that "if you opt out, Customer Data on your workspace will only be used to improve the experience on your own workspace and you will still enjoy all of the benefits of our globally trained AI/ML models without contributing to the underlying models."

Slack’s consent model seems to conflict with GDPR

Slack's privacy policy, terms, and security documentation supposedly spell out how it uses customer data. However, The Stack reported that none of those legal documents mention AI or machine learning, despite Slack debuting machine-learning features in 2016.


There's no telling yet if Slack will make any additional changes as more customers opt out. What is clear from Slack's documents is that Slack knows that its customers "have high expectations around data ownership" and that it has "an existential interest in protecting" that data.

It's possible that lawmakers will force Slack to be more transparent about changes in its data collection as the chat service continues experimenting with AI.

It's also possible that Slack already doesn't default some customers to opt into data collection for ML training. The European Union's General Data Protection Regulation (GDPR) requires informed and specific consent before companies can collect data.

"Consent cannot be implied and must always be given through an opt-in," the strict privacy law says. And companies must be prepared to demonstrate that they've received consent through opt-ins, the law says.

In the United Kingdom, the Information Commissioner's Office (ICO) requires explicit consent, specifically directing companies to note that "consent requires a positive opt-in."

"Don’t use pre-ticked boxes or any other method of default consent," ICO said. "Keep your consent requests separate from other terms and conditions."

Salesforce's spokesperson declined to comment on how Slack's policy complies with the GDPR. But Slack has said that it's committed to complying with the GDPR, promising to "update our product features and contractual commitments accordingly." That did not seem to happen when Slack AI was launched in February.

Orosz warned that any chief technology officer (CTO) or chief information officer (CIO) letting Slack slide for defaulting customers into AI training data sharing should recognize that Slack setting that precedent could quickly become a slippery slope that other companies take advantage of.

"If you are a CTO or a CIO at your company and paying for Slack: why are you still opted in?" Orosz asked on Threads. "This is the type of thing where Slack should collect this data from free customers. Paying would be the perk that your messages don’t end up in AI training data. What company will try to pull this next with customers trusting them with confidential information/data?"

This post was updated on May 17 to correct quotes from SlackHQ's posts on X.